Graphical representation of levels in a DTD
These tools are said to be able to represent, graphically, the nesting of levels of elements and sub-elements within a DTD file:
TIBCO’s TurboXML shows the structure tree and can ceate example XML files
XML Spy, but you may have to turn the DTD into a schema first.
LiveDTD provides easy navigation among the various DTD components via hyperlink. but not visualization